Method of forming screw threads



April 1 1924.

- I. c. WOODWARD METHOD OF FQRMING SCREW THREADS Patented Apr. 1, 1924.v

UNITED STATES IRVING CHARLES WOODWARD, 0F, SYRACUSE, NEW YORK.

METHOD OF FORMING SCREW THREADS.

' Application filed December 15, 1922. Serial No. 607,120.

To all :whom it may concern: I

Be it 'known that I, IRVING CHARLES WOODWARD, a citizen of the United States of 1 America, and a residentof Syracuse, county of Onondaga, and State of New York, have invented a new and useful Improvement in Methods of Forming-Screw. Threads, of which the following is a specification.

This invention relates to screw threads, and its object is to provide a method of forming a screw thread whichwill insure a perfect and tight fit with a coacting thread.

Figure 1 of the drawings shows, in section, a nut having an imperfect or incomplete thread, as formed by the first step of the rocess.

. Figure 2 illustrates the method of completing the thread.

Figure 3 shows the same section of a nut as in Figure 1, but with the thread as it would appear after performing the second step of the process.

The completed thread as shown in the drawing is standard-in every respect as to 'form, but may, when formed by the present process, be more perfect in respect to surface engagement with a coacting thread also of standard form and pitch. In many uses of coacting threaded members 1t 1s desired to have the threads fit perfectly and under sufiicient pressure all along their surfaces to effectively resist accidental motion between the coacting threaded members. It is found 'that this purpose may be attained most perfectly by a process which involves the first step of only partly forming a thread and the second step of completing the thread by application of the partly threaded article to the mate with which it coacts. The thread may be first partly formed as illustrated in Figure 1 by rolling or preferably cutting a groove 2, forming the interdental of the first step thread, the apex 3 of this interdental being of proper form for the finished thread, but the space above the apex being narrower than will be the case in the finished thread. This step of the process leaves the thread 4, with a finished base 5 of the correct angle,-but an incomplete crest 6 wider than is required for the finlshed thread and not rising as high from the base as does the finished crest. The cross sectional area 'the crest of the thread by ap of the unfinished thread, however, is equal to the desired cross sectional area ofv the finished .thread.

The second step in the process consists in applying the article having the incomplete thread to a mate 7, preferably of harder material and provided with a finished coacting thread 8. This finished coacting thread serves to crowd the material at the crest 6 of the unfinished thread upwardly so as to bring this crest to the required height and to a form properly conforming to the angles at the sides of the base of the thread. The material of the unfinished thread is in this manner caused to compensate for-any imperits surface and with sufiicient pressure to prevent accidental motion between the coacting threaded members, provided the first step' in the process offorming the thread is correctly carried out so as to leave an imperfect thread but one of cross sectional area equal to that desired in the finished thread 9. 4

I claim:

1. The method of forming a screw thread which consists in first partially forming the thread by cutting or rolling a groove in the part to be threaded, the bottom of said groove being left in the required form for the finished thread, but the top of the groove being of less widththan that required for the finished thread, and the second step of completing the thread by a squeezing and sliding, action along the sides of the thread Where y the upper portion thereof isfforced upwardly into a finished crest.

2. The process of forming a screw thread which consists in first partly forming a thread so as to provide a base for the thread of finished form but leaving the crest unfinished and wider and of less height than in the finished thread, and second forming lying the partly threaded article to anot er article made of harder material and having a fin ished thread whereby the process of formin the thread is completed by a sliding and squeezing action of the finished'thread along the sides of the unfinished thread.

3. The process of forming a screw thread whichconsists in-first forming on an. article to be threaded,-an incomplete thread having a uniform, pitch and. sufficient volume to form a 'full thread,-but beingimperfect as 6 to height :andwidth at the crest, and second, .forcing ls'aid imperfect thread into engagement with a mating part having a complated thread whereby the part serves as aforming device for completing the imperfect thread by sliding pressure along the sides of the imperfect thread.

Signed at Syracuse this seventh day of December, 1922.

IRVING CHARLES WooD ARn. 

